1. Field of the Invention
The present invention relates to an electroconductive member adaptable to a charging member, a developer carrier, a transfer member, or the like disposed adjacent to an image carrier in an electrophotographic image forming apparatus such as a copying machine, a laser beam printer, or a facsimile, a process cartridge including the electroconductive member, and an image forming apparatus including the process cartridge.
2. Description of Related Art
An electrophotographic image forming apparatus such as a copying machine, a laser beam printer, or a facsimile has been conventionally provided with a charging member that performs an electrification process on an image carrier (or an electrostatic latent image carrier or a photoconductor), and a transfer member that performs a transfer process on toner on the photoconductor. An electroconductive member is used as the charging member or the transfer member. A case using the electroconductive member as the charging member is mentioned hereinafter.
FIG. 1 is a schematic illustration of an electrophotographic image forming apparatus. In FIG. 1, reference numeral 11 denotes an image carrier or a photoconductor on which an electrostatic latent image is formed; 12, a charging member or a charger roller that performs an electrification process, disposed in contact with or in proximity to the image carrier 11; 13, light for exposure, such as laser light or reflected light from an original; 14, a toner carrier or a developing roller that causes toner 15 to adhere to the electrostatic latent image on the image carrier 11; 16, a transfer member (or a transfer roller) that transfers a toner image on the image carrier 11 to a recording medium 17; and 18, a cleaning member or a blade for cleaning the image carrier 11 after the transfer process.
Reference numeral 19 denotes waste toner discharged by the cleaning member 18 removing the toner remaining on the image carrier 11; 201, a developing unit; and 211, a cleaning unit.
Incidentally, functional units generally required for other electrophotography processes are omitted from FIG. 1, because they are not necessary for explanation.
The image forming apparatus as mentioned above is configured to form an image through the following processes.
1. The charger roller 12 electrifies the surface of the image carrier 11 at a desired potential.
2. An exposure unit projects image light onto the image carrier 11 to form on the image carrier 11 an electrostatic latent image corresponding to a desired image.
3. The developing roller develops the electrostatic latent image by the toner to form a toner image or a developed image on the image carrier 11.
4. The transfer roller 16 transfers the toner image on the image carrier 11 to the recording paper 17.
5. The cleaning unit 18 cleans off the toner remaining on the image carrier 11 without being transferred.
6. The transfer roller 16 carries to a fixing unit (not shown) the recording paper 17 having the toner image transferred thereto. The fixing unit applies heat and pressure to the toner to fix the toner onto the recording paper 17.
The above procedure 1 to 6 is repeated to form a desired image on the recording paper 17.
Conventional electrification methods using the charger roller include a contact electrification method that involves bringing the charger roller into contact with the image carrier. The conventional contact electrification method has the following problems (1) to (5).
(1) The charger roller leaves its track on the surface of the image carrier since a constituent substance of the charger roller seeps out of the charger roller onto the surface of the charged image carrier.
(2) Static crackling is emitted since the charger roller in contact with the charged image carrier vibrates when subjected to an alternating voltage.
(3) The charger roller undergoes deterioration in electrification performance since the toner on the image carrier adheres to the charger roller (or, in particular, the above-mentioned seepage increases the likelihood of adhesion of the toner).
(4) The constituent substance of the charger roller adheres to the image carrier.
(5) The charger roller undergoes permanent deformation when the image carrier is not in use for a long time.
As a method for solving the above problems, there is proposed a proximity electrification method that involves bringing the charger roller into proximity with the image carrier, as disclosed in JPA No. 3-240076 (Patent Document 1), JPA No. 2001-312121 (Patent Document 2), JPA No. 2005-91818 (Patent Document 3), and so on. The method electrifies the image carrier by applying a voltage to the charger roller disposed as facing the image carrier with a distance or a gap of 50 to 300 μm between when the charger roller and the image carrier are in closest proximity to each other. Because of providing no contact between a charger unit and the image carrier, the proximity electrification method does not present the problems inherent in a contact charger unit, that is, “the adhesion of the constituent substance of the charger roller to the image carrier” and “the permanent deformation caused by the image carrier being in its stopped state for a long time.” As for “the deterioration in the electrification performance due to the adhesion of the toner or the like on the image carrier to the charger roller,” the proximity electrification method is superior in electrification performance because of reducing the toner adhering to the charger roller.
At this point, a non-contact electrification method is more excellent than the contact electrification method. Because of using corona discharge following Paschen's law between the charger roller and the image carrier to electrify the surface of the photoconductor, however, both the methods produce or generate oxidative gases such as ozone or NOx, thus leading to deterioration in the surfaces of the image carrier and the charger roller with time. The deterioration increases the likelihood of adhesion of the toner and its constituent substance to the surface of the charger roller, thus leading to the deterioration in the electrification performance of the charger roller. The deterioration results in deterioration of the electrification performance of the image carrier, or the like, thereby increasing the likelihood of image degradation.